Many gases, such as methane, nitrogen, and natural gas, are stored at temperatures far below the usual ambient temperatures so that they may be kept in a liquid form. This permits large quantities of the gas to be stored in an otherwise limited volume of space. Such low temperature liquefied gases are usually not maintained at high pressure, but rather are maintained at about atmospheric pressure or under a relatively low pressure. Thus, the storage tank or facility need not be designed for great internal pressure.
Precast, prestressed concrete tanks are well-known for storage of liquefied gases, for example, as described in U.S. Pat. Nos. 3,092,933, 3,633,328, and 3,488,972, all to Closner et al. and assigned to Preload Corp. Typically, precast, prestressed concrete tanks have an inner wall defining a primary tank, and an outer wall defining a secondary tank. The outer wall is prestressed by an application of wire windings under tension around the outer wall. The inner wall is typically constructed of 9% nickel steel or some other type of steel suitable for use at cryogenic temperatures. In some cases, the inner tank may also be precast, prestressed concrete.
During construction of precast, prestressed concrete tanks, when the outer wall is built first, the inner wall must either be inserted through an opening in the top of the tank, or by tunneling underneath the foundation to insert the inner wall from beneath the tank. However, these conventional construction practices for precast, prestressed concrete tanks are complicated and undesirable.
There is a continuing need for a precast, prestressed concrete tank and method that facilitates construction of a primary tank within a secondary tank. Desirably, the precast, prestressed concrete tank and method permits for the construction of the inner wall after the outer wall has been erected, but without requiring insertion through a top of the outer wall, or by tunneling underneath the outer wall.